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High pressure synthesis and stability of cobalt hydrides

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https://aip.scitation.org/doi/full/10.1063/1.5026535
Original languageEnglish
JournalThe Journal of Chemical Physics
DOIs
Publication statusPublished - 13 Apr 2018

Abstract

In-situ high-pressure high-temperature X-ray powder diraction studies of the cobalt-hydrogen system reveal the direct synthesis of both the binary cobalt hydride (CoH), and a novel cobalt dihydride (CoH2). We observe
the formation of fcc CoH at pressures of 4 GPa, which persists to pressures of 45 GPa. At this pressure, we see the emergence with time of a further expanded fcc lattice, which we identify as CoH2, where the hydrogen
atoms occupy the tetrahedral vacancies. We have explored alternative synthesis routes of CoH2, and can lower the synthesis pressure to 35 GPa by the application of high temperature. CoH2 is stable to at least
55 GPa, and decomposes into CoH below 10 GPa, releasing molecular hydrogen before further decomposing completely into its constituent elements below 3 GPa. As a first-row transition metal, cobalt has a relatively
lower mass than other hydride-forming transition metals, and as a result CoH2 has a high hydrogen content of 3.3 wt% and a volumetric hydrogen density of 214 g/L.

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